1. Field of the Invention.
The present invention relates to the field of electrical device packaging, and more particularly, to the packaging and mounting of electronic devices such as integrated circuits.
2. Prior Art.
There are many forms of packaging for electronic devices which are well known in the prior art. The fundamental requirements for such packages include mechanical and environmental protection for the electronic device and ease of incorporating into a circuit, such as a printed circuit. Other requirements may include shielding of the device from stray electric and magnetic fields and cooling of devices of high power dissipation.
In recent years, integrated circuit complexity has greatly increased, and wherever possible package sizes have tended to decrease. With certain integrated circuits, particularly integrated circuits using field effect devices, the power dissipation is extremely low, so that package sizes and packaging densities are limited in substantial part by one's ability to produce and utilize such packages on a practical basis, and of course to provide cooling when such packages are used in very high density systems. Thus, from a user's standpoint, the circuit should be removable and replaceable from a printed circuit board without requiring soldering operations and should occupy a minimum circuit board area consistent with present capabilities in terms of printed circuit board conductor size and lead requirements. Similarly, the height of the package should be held to a minimum to allow the close packing of adjacent circuit boards while still providing the air flow space therebetween.
One prior package which has been used to package integrated circuits utilizes a chip carrier, typically ceramic, having a pocket therein for receiving the integrated circuit and having a plurality of conductive regions extending into the cavity for connection to the chip. The conductive regions extend outward to the edges of the chip carrier, each connecting to one of a plurality of conductive regions extending down the side of the chip carrier exposed so as to be electrically contactable from the side of the chip carrier. A cover seals the cavity on the chip carrier to provide the ultimate mechanical and environmental protection for the electronic device (e.g. chip).
For mounting an assembled chip carrier to a printed circuit, a molded plastic connector having a plurality of individual leads is first soldered to the circuit board. The individual leads extend upward into the sides of a cavity in the top face of the connector so as to form spring contacts for contacting the conductive regions at each side of the chip carrier. Thus the chip carrier can be placed into and taken out of the mating connector to allow individual circuit testing or replacement, with the chip carrier being held into the connector by a separatre locking member extending over the chip carrier and being retained at each end of the connector.
This type of package has a number of advantages over other packages such as the dual in-line packages, since it allows the removal of the circuit without soldering operations, is reasonably small and has reasonably good contact reliability because of the wiping action of the contacts when a chip carrier is inserted. However, the overall height of the connector is greater than may be necessary, as the chip carrier is inserted blow the top surface thereof, and a separate locking element extends thereabove, serving no purpose other than to retain the chip carrier in position. Also, the spring contacts on the connector are limited in the contact pressure they may exert, as the chip carrier must be inserted and removed against the frictional force created by the contacts. This presents a limitation, particularly for removal purposes, as some means must be provided to release the contact pressure or force the chip carrier out of the connector in opposition to the frictional forces. Further, there is a long wiping action between the spring contacts and the chip carrier otherwise unnecessary for proper contact.